Building up the Strength

I'm aiming to complete my first tri in the Spring of next year. This is something I've always wanted to do, but have always made excuses. I'm finally completely committing to this and I'm looking for some support online because I don't know anyone in my area that does this kind of thing.
One of my main concerns is that I have pretty bad knees. I've been in physical therapy before. The problem is the ligaments around my kneecaps are very loose. Does anybody have any tips of how to build up to have the strength? Any specific training workouts that people want to share? I've been out of shape for a while. I'm not looking to "just finish" either. I would really like to make this into a hobby and love, not just something that I do once.
I've been reading the threads for awhile and I really enjoy the community that you all have here. :)
Thanks, Ladies!!

Welcome to the forums, and good luck on your training!
I competed in my first Tri in June, and did my second one last week. I'm hooked! I have had "bad knees" most of my life - too many years as a catcher growing up, and pretty much every one of my joints are loose (always going to the Chiro to put things back in place, even ribs!).
Through out the years, I've always been told to focus on building strength around them to help hold them in place - calf raises, quad and hamstring exercises, ad/abductor exercises; and I'm very mindful of keeping things even and not overbuilding one muscle group to where it pulls the knee cap out of place. Maybe I've been lucky or just really cautious, because (knock on wood), the last couple years they've been really good, though that's only since I've been really good about keeping them healthy and strong (I'm 35). No issues in my tris, I play softball weekly, so I've got a lot of side to side sprinting motions, I hike - you name it, I do. Occasionally if I lack my strength training, I will feel it; the knee caps get loose and slip side to side, and I lose strength in my running because of that weak link.
It doesn't take much time, or a lot of weight to be effective. My legs are far from "cut" :) But the hour or so a week I take to do my little exercises really pays off (I am more or less maintaining right now). My Chiro can tell when I haven't been doing them, as she does full body adjustments, so when she gets to my knees and twists them and they "give", she GIVES me crap!
I use a lower weight that what I would use to bulk up, especially at first, so as not to over stress the joint; like I said, all mine are loose and I have a problem hyperextending things. I do 3 sets of 12-15 reps on the quad and hamstring machines paying special attention to form - don't fling the machine; and I go slow, too, really concentrating on constricting the muscle to move the weight rather than speed. To balance it out, I also use the adductor and abductor machine to work the inside and outside of my legs, and do calf raises in three different positions (straight, heels turned out, and heels turned in). I started out doing this three times a week. Now I just maintain. My summers are typically spent outside doing stuff, and winters are spent rebuilding strength for the next season, so once it starts to cool off and get dark earlier, and I'm stuck inside, I'll do more strength training to prepare a good base for next season.
Now is a good time to start for you since your goal is for next season. Plenty of time for you to get those knees into shape! Just take it easy, and listen to your body. I spent the better part of my life not doing things because of my knees. Now I rarely think of them (they let me know if I forget them for too long).
Good luck!